Driving force transmitting device for vehicle

ABSTRACT

A driving force transmitting device for a vehicle includes a drive mode-shifting mechanism which is disposed in the final drive gear-set of a vehicle. The drive mode-shifting mechanism includes a first rotating member, a second rotating member, a third rotating member, and a movable member. The movable member is movable between a first position in which the first and second rotating members are disconnected to effect the two-wheel-drive mode, a second position in which the first and second rotating members are connected to effect differential-free four-wheel-drive mode, and a third position in which the second and third rotating members are connected to effect the differential-lock four-wheel-drive mode.

[0001] This application is based on and claims priority under 35 U.S.C.§119 with respect to Japanese Application No. 11(1999)-200021 filed onJul. 14, 1999 and Japanese Application No. 2000-212515 filed on Jul. 13,2000, the entire content of both of which is incorporated herein byreference.

FIELD OF THE INVENTION

[0002] The present invention generally relates to a driving forcetransmitting device for a vehicle. More particularly, the presentinvention pertains to a driving force transmitting device including adrive mode-shifting mechanism which shifts the drive mode between atwo-wheel drive mode, a differential free four-wheel drive mode, and adifferential lock four-wheel drive mode.

BACKGROUND OF THE INVENTION

[0003] A conventional driving force transmitting device for a vehicle isdisclosed in Japanese Patent Application Laid-Open Publication No. Hei 8(1996)-85355. This device includes a first sleeve connected to the outercircumference of the right drive shaft and movable axially via a splineengagement, a second sleeve connected to the outer circumference of thefirst sleeve and axially movable via a spline engagement, a firstdog-clutch device formed on the right side gear of the differential gearand the first sleeve to connect and disconnect the right side gear andthe first sleeve in response to axial movement of the first sleeve, anda second dog-clutch device formed on the casing of the differential gearand the second sleeve to connect and disconnect the casing and thesecond sleeve in response to axial movement of the second sleeve. Withthis device, when the first sleeve is disconnected from the right sidegear and the second sleeve is disconnected from the casing, thetransmission of the driving force between the right and left driveshafts and the propeller or drive shaft is prohibited, and a two-wheeldrive mode is thus established. When the first sleeve is connected tothe right side gear and the second sleeve is disconnected from thecasing, the transmission of the driving force between the right and leftdrive shafts and the drive shaft is allowed with functional operation ofthe differential gear, and so a differential-free four wheel drive modeis established. Further, when the first sleeve is connected to the rightside gear and the second sleeve is connected to the casing, thetransmission of the driving force between the right and left driveshafts and the drive shaft is allowed while prohibiting the functionaloperation of the differential gear, and so a differential-lock fourwheel drive mode is established.

[0004] In the above-described device, however, two sleeves are requiredfor shifting the drive mode between the three drive modes. Namely, thefirst sleeve shifts the drive mode between the two-wheel drive mode andthe differential free four-wheel drive mode, and the second sleeveshifts the drive mode between the differential free four-wheel drivemode and the differential lock four-wheel drive mode under the firstsleeve-on condition. Therefore, the number of the component increasesand the complexity of the structure of the device is increased.

[0005] Further, because two actuators are required for operating thesleeves, the overall size of the system, including the transmittingdevice and the actuators, is increased and the manufacturing cost of thetransmitting device is also increased.

[0006] In light of the foregoing, a need exists for a driving forcetransmitting device that does not suffer from the foregoingdisadvantages and drawbacks.

[0007] It would thus be desirable to provide a driving forcetransmitting device for a vehicle which is able to shift the drive modebetween three drive modes without increasing the manufacturing cost, thenumber of components and the complexity of the overall device.

SUMMARY OF THE INVENTION

[0008] According to one aspect of the present invention, a driving forcetransmitting device for a vehicle includes a housing in which aredisposed a differential gear connected to a pair of wheels and adrive-mode-shifting mechanism. The drive-mode-shifting mechanismincludes a first rotating member forming an output member of thedifferential gear for one wheel side, a second rotating member rotatablerelative to the first rotating member and rotatable together with one ofthe wheels, a third rotating member rotatable together with a casing ofthe differential gear to which driving force is transmitted from a powersource, and a movable member. The movable member is movable between afirst position in which the first and the second rotating members aredisconnected to effect the two-wheel-drive mode, a second position inwhich the first and the second rotating members are connected to effectthe differential-free four-wheel-drive mode, and a third position inwhich the first, the second and the third rotating members are connectedto effect the differential-lock four-wheel-drive mode.

[0009] When the movable member is positioned to disconnect theconnection between the first and the second rotating members (i.e., thetwo-wheel-drive mode), the casing and the third rotating member rotatetogether in response to the driving force transmitted from the powersource. An output member of the differential gear for another wheel sidedoes not transmit the driving force from the power source to anotherwheel because the output member of the differential gear for one wheelside is disconnected from one wheel.

[0010] When the movable member is positioned to connect the first andsecond rotating members and disconnect the connection between the firstand third rotating members (i.e., the differential-free four-wheel-drivemode), the third rotating member rotates together with the first andsecond rotating members, and the output member of the differential gearfor another wheel side transmits power from the power source. In thismode, the difference in rotational speed between the one wheel andanother wheel is absorbed because the first rotating member is connectedwith the output member of another wheel side through the differentialgear. Furthermore, when the movable member connects the first and secondrotating members and connects the first and third rotating members(i.e., the differential-lock four-wheel-drive mode), the pair of wheelsrotates at the same rotation speed because the first, second and thirdrotating members are locked, and power is transmitted to the pair ofwheels from the power source. Accordingly, it is possible to shift thedrive mode between the two-wheel drive mode, the differential-freefour-wheel-drive mode and the differential-lock four-wheel drive modethrough the operation of the movable member.

[0011] According to another aspect of the present invention, a drivingforce transmitting device for a vehicle includes a housing in which aredisposed a differential gear connected to a pair of wheels and adrive-mode-shifting mechanism. The drive-mode-shifting mechanismincludes a first rotating member rotatable in response to the drivingforce transmitted from a power source, a second rotating memberrotatable together with a casing of the differential gear, a thirdrotating member forming an output member for the differential gear androtatable together with the one wheel, and a movable member shiftablebetween a first position in which the first and second rotating membersare disconnected to effect the two-wheel-drive mode, a second positionin which the first and second rotating members are connected to effectdifferential-free four-wheel-drive mode, and a third position in whichthe first and third rotating members are connected to effect thedifferential-lock four-wheel-drive mode.

[0012] When the movable member disconnects the connection between thefirst and second rotating members (i.e., the two-wheel-drive mode), thedriving force from the power source is not transmitted to the pair ofwheels because the driving force from the power source is nottransmitted to the casing of the differential gear. When the movablemember connects the first and second rotating members and disconnectsthe first and third rotating members (i.e., the differential-freefour-wheel-drive mode), the driving force from the power source istransmitted to the pair of wheels through the differential gear, becausethe first rotating member rotates together with the casing through thesecond rotating member. In this mode, the difference in rotational speedbetween the one wheel and another wheel is absorbed by the differentialgear. Further, when the movable member connects the first and secondrotating members and connects the first and third rotating members(i.e., the differential-lock four-wheel-drive mode), the pair of wheelsrotates at the same rotation speed because the first, second and thirdrotating members are locked and power from the power source istransmitted to the pair of wheels. Accordingly, it is possible to shiftthe drive mode between the two-wheel drive mode, the differential-freefour-wheel drive mode and the differential-lock four-wheel drive mode bythe operation of movable member.

[0013] In the present invention, it is possible to shift between thethree drive modes by shifting a single movable member between the firstposition, the second position and the third position. Accordingly, thedrive mode-shifting mechanism can be constructed and controlled in arather simple manner. Further, it is possible to reduce themanufacturing cost of the drive mode-shifting mechanism.

[0014] The differential referenced herein refers to a differentialassembly for absorbing the difference in rotational speed between thepair of wheels to permit smooth driving. The differential can be alimited slip differential. The final drive gearset referenced hereinrefers to the final drive/differential assembly.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0015] The foregoing and additional features and characteristics of thepresent invention will become more apparent from the following detaileddescription considered with reference to the accompanying drawingfigures in which like elements are designated by like reference numeralsand wherein:

[0016]FIG. 1 is a schematic illustration of a portion of a vehicleprovided with a driving device that includes a drive mode-shiftingmechanism in accordance with the present invention;

[0017]FIG. 2 is a cross-sectional view of the main portions of the drivemode-shifting mechanism according to a first embodiment of the presentinvention;

[0018]FIG. 3 is a cross-sectional view of the main portions of the drivemode-shifting mechanism according to a second embodiment of the presentinvention; and

[0019]FIG. 4 is a side view of the drive mode-shifting mechanism shownin FIG. 3 as seen from the direction of the arrow A in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A vehicle equipped with a driving force transmitting device inaccordance with the present invention is schematically shown in FIG. 1.In the various embodiments of the present invention discussed below, thevehicle is a rear wheel drive vehicle in which engine power istransmitted to the rear wheels at all times. In the two-wheel-drivemode, power transmission to the front wheels is interrupted.

[0021] Referring to FIG. 1, the vehicle includes an engine 1 whichserving as a power source, a transmission 2 connected to the output ofthe engine 1, a drive axle 3 having one end connected to the output sideof the transmission 2 for transmitting power from the engine 1, and apair of final drive gear-sets 4, 10 having differential gears inside andeach disposed on one end of the drive axle 3. In addition, a pair offront axles 5, 7 is connectable to the output of the differential gear20 (shown in FIG. 2) in the final gear-set 4 and respective front wheels6,8 are attached to each of the front axles 5, 7 . A pair of rear axles11, 13 is connected to the output of the differential gear in the finalgear-set 10 and a respective rear wheel 12, 13 is attached to each ofthe rear axles 11, 13.

[0022] The driving force inputted from the drive axle 3 to the finalgear-set 10 is transmitted to the pair of rear wheels 12, 14 at alltimes. Driving power inputted from the drive axle 3 to the finalgear-set 4 is transmitted to the front wheels 6, 8 by operation of thedrive mode-shifting mechanism 50 shown in FIG. 2.

[0023] Referring to FIG. 2, the differential gear 20 in the finalgear-set 4 includes a pair of side gears 21, 22 formed in the samegeneral direction of the front axles 5,7 and each composed of an outputportion operatively associated with the respective front axle 5, 7. Thedifferential gear 20 also includes a pair of pinion gears 23, 24engaging the side gears 21, 22 respectively and formed generally in adirection perpendicular to the front axles 5, 7. The differential gear20 is housed in a casing 25 for rotation in the same direction as thefront axles 5, 7. The casing 25 forms a ring gear 25 b engaging a piniongear 27 a formed on the end of an input shaft 27 which transmits therotation of the drive axle 3 to the casing 25 via a yoke 26. An outputshaft 31 which engages the side gear 21 by way of a spline is connectedto the front axle 5 via a ball joint 28.

[0024] The drive mode-shifting mechanism 50 is formed in the finalgear-set 4 and includes a first rotating member constituted by the sidegear 22 which is the output to the front wheel 8, a second rotatingmember 32 rotatable together with the front wheel 8 and located at theaxial end of the first rotating member 22 for rotating relative to thefirst rotating member 22, a third rotating member 25A constituting partof the casing 25 which rotates in accordance with the rotation of theinput shaft 27, a sleeve 41 constituting a movable member that ismovable between a first position in which the first rotating member 22and the second rotating member 32 are disconnected to effect thetwo-wheel-drive mode, a second position for connecting the firstrotating member 22 and the second rotating member 32 to effectdifferential-free four-wheel-drive mode, and a third position forconnecting the second rotating member 32 and the third rotating member25A to effect the differential-lock four-wheel-drive mode, and anactuator 42 for moving the sleeve 41 in the axial direction between thefirst, second and third positions . The sleeve 41 and the actuator 42form a shifting device 40. The second rotating member 32 is disposed ina housing 29 at a position adjacent the axial end of the first rotatingmember 22. The end of the second rotating member 32 is connected withthe front axle 7 via a ball joint 30.

[0025] The outer surface of the first rotating member 22 is providedwith a first spline 22 a, the outer surface of the second rotatingmember 32 is provided with a second spline 32 a, and the inner surfaceof the third rotating member 25A is provided with a third spline 25 a.The cross-sectional shape of the first spline 22 a and the second spline32 a is substantially same. Further, the third spline 25 a opposes thefirst spline 22 a generally in the radial direction. The sleeve 41possesses a cylindrical hollow shape and is provided with splines on itsinner surface and its outer surface which are engageable with the firstspline,22 a, the second spline 32 a and the third spline 25 a. In thepresent invention, the first spline 22 a rotates together with thesecond spline 32 a by moving the sleeve 41 in the axial direction.

[0026] The actuator 42 which moves the sleeve 41 in the axial directionincludes or is operatively associated with an electric motor thatrotates according to the supplied current, a reduction gear that reducesthe output of the electric motor, an output gear for transmitting theoutput from the reduction gear via a spiral spring, and a rack 44transforming the rotation of the output gear into movement in the axialdirection. The rack 44 is slidably movable on the outer surface of ashaft 46 which is installed in the housing 29. The operation of themotor is controlled by an electric control unit (ECU). The driving forceof the motor is transmitted to the output gear via the reduction gearand the spiral spring, and the rack 44 moves in the axial direction inaccordance with the rotation of the output gear. This thus causes a forkmember 45 which fixed on the rack 44 to also move in the axialdirection. Accordingly, it is possible to engage the sleeve 41 mountedon the end of the fork 45 with each of the splines 22 a, 32 a, 25 a byaxially moving the fork 45.

[0027] With the vehicle in the two-wheel-drive mode, the sleeve 41 islocated at the left end of FIG. 2 shown in solid line which constitutesthe first position. At the first position, the sleeve 41 engages thefirst rotating member 22 but does not engage the second rotating member32. Driving torque from the engine 1 is transmitted to the casing 25from the transmission 2 via the drive axle 3, the yoke 26 and the inputshaft 27. However, the first rotating member 22 rotates only itselfbecause the first rotating member 22 is not engaged with the front axle7. In this way, the two-wheel-drive mode is performed because thedriving force from the drive axle 3 is not transmitted to the front axle7.

[0028] When the vehicle shifts to the differential-free four-wheel-drivemode from the two-wheel-drive mode, the sleeve 41 engages the secondspline 32 a and the first spline 22 a as a result of sliding movement ofthe sleeve 41 towards the center portion shown in broken line in FIG. 2.This constitutes the second position of the sleeve 41. At the secondposition, the sleeve 41 does not engage the third spline 25 a. It is tobe noted that when the phase or rotation of the first spline 22 adiffers from the phase or rotation of the second spline 32 a, the sleeve41 cannot move to engage with the first spline 22 a, and the spiralspring is compressed in spite of driving the motor. When the phase ofthe first spline 22 a moves into harmonization with the phase of thesecond spline 32 a, the sleeve 41 is able to move axially and engage thefirst spline 22 a. Driving torque from the engine 1 is thus transmittedto the casing 25 from the transmission 2 via the drive axle 3, the yoke26 and the input shaft 27. Further, driving torque from the engine 1 istransmitted to the front wheels 6, 8 from the side gears 21, 22 asoutput of the differential gear 20 via the transmission 2 and the frontaxles 5, 7. When the vehicle is turning, rotation differences aregenerated between the left side front wheel 8 and the right side frontwheel 6. However, these rotation differences are absorbed by therotation of the side gears 21, 22 and the pinion gears 23, 24 themselvesand so it is possible to smoothly drive the vehicle.

[0029] When the vehicle shifts to the differential-lock four-wheel-drivemode from the differential-free four-wheel-drive mode, the sleeve 41engages the second spline 32 a and the first spline 22 a throughmovement of the sleeve 41 toward the right end in FIG. 2. This positionof the sleeve 41 is shown in broken line in FIG. 3 and constitutes thethird position of the sleeve 41. At the third position, the spline onthe outer surface of the sleeve 41 engages the third spline 25 a. Thefront axles 5, 7 and the casing 25 are thus locked-up and rotatetogether as a unit. Driving torque from the engine 1 is transmitted tothe front wheels 6, 7 from the transmission 2 via the drive axle 3, theyoke 26, the input shaft 27, the casing 25 and the front axles 5, 7. Inthis condition, the capability for running progresses because thedifferential gear 20 does not operate and the front wheels 6, 8 rotatetogether or as a unit if one of the front wheels 6, 8 does not contactthe road or travels into a muddy area for example.

[0030] According to the first embodiment, when the splined shafts areout of phase with one another, the sliding movement of the sleeve 41 islimited through use of the spiral spring. It is to be understood,however, that the use of the spiral spring is not essential to thepresent invention. Rather, any type of mechanism may be used as long asthe sleeve 41 is inhibited from sliding before the splines are locatedin phase with one another. Further, it is possible to use a mechanismdifferent from the motor actuator 42. for sliding the sleeve 41, such asone involving a manual lever.

[0031] A second embodiment of the present invention is explained belowwith reference to the illustrations FIGS. 3 and 4. FIG. 3 is across-sectional view of the main portions of the drive mode-shiftingmechanism 100 according to the second embodiment while FIG. 4illustrates a shifting device 90 including a movable member 91 of thedrive mode-shifting mechanism 100.

[0032] As shown in FIG. 3, the drive mode-shifting mechanism 100includes a first rotating member 74 as a ring gear which rotates in thesame direction as the output of a differential gear 70, a secondrotating member 75A formed as part of a casing 75 of the differentialgear 70 and rotatable relative to the first rotating member 74, a thirdrotating member 73 which is an output of the differential gear 70, and asleeve 91 functioning as a movable member. The sleeve or movable member91 is movable between a first position in which the first and secondrotating members 74, 75A are disconnected to effect the two-wheel-drivemode, a second position in which the first and second rotating members74, 75A are connected to effect the differential-free four-wheel-drivemode, and a third position in which the first and third rotating members74, 73 are connected to effect the differential-lock four-wheel-drivemode.

[0033] The first rotating member 74 is the ring gear engaging a piniongear 77 a of an input shaft 77, with a first spline 74 a being formed inthe inner surface of the first rotating member 74. The second rotatingmember 75A is a part of the casing 75, and a second spline 75 a isformed on the inner surface of the rotating member 75A in opposingrelation to the first spline 74 a with respect to the radial direction.The third rotating member 73 is spline engaged with the outer surface ofthe output shaft 81 which rotates together with the side gear 71 as anoutput of the differential gear 70. A third spline 73 a having the sameshape as the second spline 75 a is formed on the outer surface of thethird rotating member 73. An actuator 92 is operatively associated withthe sleeve 91 to move the sleeve 91 in the axial direction. The shiftingdevice 90 is comprised of the sleeve 91 and the actuator 92.

[0034] The sleeve 91 is formed as a generally cylindrical hollow-shapedelement with splines formed on its outer and inner surface to engage thesplines 74 a, 75 a, 73 a. The sleeve 91 slides along the axial directionof the first, second and third rotating members 74, 75, 73. Thestructure and operation of the actuator 92 is the same as that describedabove in connection with the first embodiment and so a detaileddescription is not repeated here.

[0035] When the vehicle is in the two-wheel-drive mode, the sleeve 41 islocated at the left end of FIGS. 3 and 4 and is shown in solid lines. Inthis first position of the sleeve 91, the spline on the inner surface ofthe sleeve 91 does not engage the second spline 75 a. Accordingly,rotation of the ring gear (the first rotating member) 75 b is nottransmitted and so while the rear wheels are driven, the front wheelsare not so that they simply rotate following the rear wheels.

[0036] When the vehicle shifts to the differential-free four-wheel-drivemode from the two-wheel-drive mode, the sleeve 91 slides toward thecenter portion in FIGS. 3 and 4 by operation of the actuator 92 by wayof the fork 95. At this center position constituting the secondposition, the spline on the outer surface of the sleeve 91 engages thefirst spline 74 a and the spline on the inner surface of the sleeve 91engages the second spline 75 a. Therefore, the casing 25 rotates byvirtue of the transmission of the rotation of the drive axle to thecasing 25 via the ring gear 75 b. The driving force is thus transmittedto the front wheels upon becoming shifted to the differential-freefour-wheel-drive mode from the two-wheel-drive mode, and thedifferential gear 70 is rendered operational.

[0037] When the vehicle shifts to the differential-lock four-wheel-drivemode from the differential-free four-wheel-drive mode, the sleeve 91 ismoved to the right end from the center portion in FIGS. 3 and 4 throughoperation of the actuator 92 by way of the fork 95. In this thirdposition of the sleeve 91, the spline on the outer surface of the sleeve91 engages the first spline 74 a and the spline on the inner surface ofthe sleeve 91 engages the second spline 75 a and the third spline 73 a.In this condition, the ring gear 75 b, the casing 75 and one of the sidegear 71 of the differential gear 70 are locked up and rotate as a unit.The device is thus shifted to the differential-lock four-wheel-drivemode from the differential-free four-wheel-drive mode in which thedifferential gear 70 is not operational.

[0038] The second embodiment of the present invention is advantageous inthat the power loss can be lessened as compared to the vehicle describedin the first embodiment because the rotation of the drive axle is nottransmitted to the casing 75 during the two-wheel-drive mode.

[0039] In accordance with the present invention, it is possible to shiftbetween three drive modes by moving the one movable member between thefirst position, the second position and the third position. Accordingly,the drive mode-shifting mechanism can be constructed and controlled in arelatively simple manner. Further, it is possible to prevent an increasein the cost of the drive mode-shifting mechanism.

[0040] In the first and second embodiments of the present invention, itis also possible to shorten the length of the differential with respectto the width direction of the vehicle because the first spline is formedso as to oppose the third spline with respect to the radial direction.That is, the first rotating member is disposed around the third rotatingmember so as to overlap with respect to the axial direction.

[0041] The principles, preferred embodiments and modes of operation ofthe present invention have been described in the foregoingspecification. However, the invention which is intended to be protectedis not to be construed as limited to the particular embodimentsdescribed. Further, the embodiments described herein are to be regardedas illustrative rather than restrictive. Variations and changes may bemade by others, and equivalents employed, without departing from thespirit of the present invention. For example, it is possible to connecteach rotating member by using a dog clutch instead of the spline.

What is claimed is:
 1. A driving force transmitting device for vehiclecomprising: a housing in which are disposed a differential gearconnected to a pair of wheels and a drive-mode-shifting mechanism; andthe drive-mode-shifting mechanism including a first rotating memberforming an output member of the differential gear for one wheel side, asecond rotating member rotatable relative to the first rotating memberand rotatable together with one of the wheels, a third rotating memberrotatable together with a casing of the differential gear to which adriving force is transmitted from a power source, and a movable membermovable between a first position in which the first and the secondrotating members are disconnected to effect a two-wheel-drive mode, asecond position in which the first and the second rotating members areconnected to effect a differential-free four-wheel-drive mode, and athird position in which the first, the second and the third rotatingmembers are connected to effect a differential-lock four-wheel-drivemode.
 2. A driving force transmitting device for vehicle according toclaim 1, wherein the first, the second and the third rotating membersare disposed coaxially.
 3. A driving force transmitting device forvehicle according to claim 2, wherein the movable member moves in anaxial direction of the first, the second and the third rotating members.4. A driving force transmitting device for vehicle according to claim 3,wherein the first rotating member has a surface provided with a firstspline, the second rotating member has a surface provided with a secondspline, the third rotating member has a surface provided with a thirdspline, and the movable member is provided with a shift splineengageable with the first, the second and the third splines.
 5. Adriving force transmitting device for vehicle according to claim 4,wherein the first spline is provided on an outer surface of the firstrotating member, the second spline is provided on an outer surface ofthe second rotating member, the third spline is provided on an innersurface of the third rotating member, the first spline possesses across-sectional shape that is the same as the cross-sectional shape ofthe second spline, and the third spline is disposed on an outercircumference of the first spline.
 6. A driving force transmittingdevice for vehicle comprising: a housing in which are disposed adifferential gear connected to a pair of wheels and adrive-mode-shifting mechanism, the drive-mode-shifting mechanismincluding a first rotating member rotatable in response to a drivingforce transmitted from a power source, a second rotating memberrotatable together with a casing of the differential gear, a thirdrotating member forming an output member for the differential gear androtatable together with one wheel, and a movable member shiftablebetween a first position in which the first and second rotating membersare disconnected to effect a two-wheel-drive mode, a second position inwhich the first and second rotating members are connected to effect adifferential-free four-wheel-drive mode, and a third position in whichthe first and third rotating members are connected to effect adifferential-lock four-wheel-drive mode.
 7. A driving force transmittingdevice for vehicle according to claim 6, wherein the first, the secondand the third rotating members are disposed coaxially.
 8. A drivingforce transmitting device for vehicle according to claim 7, wherein themovable member moves in an axial direction of the first, the second andthe third rotating members.
 9. A driving force transmitting device forvehicle according to claim 8, wherein the first rotating member has asurface provided with a first spline, the second rotating member has asurface provided with a second spline, the third rotating member has asurface provided with a third spline, and the movable member is providedwith a shift spline engageable with the first, the second and the thirdsplines.
 10. A driving force transmitting device for vehicle accordingto claim 9, wherein the first spline is provided on an inner surface ofthe first rotating member, the second spline is provided on an outersurface of the second rotating member, the third spline is provided onan outer surface of the third rotating member, the second splinepossesses a cross-sectional shape that is the same as thecross-sectional shape of the third spline, and the first spline isdisposed on an outer circumference of the second spline.
 11. A drivingforce transmitting device for vehicle comprising: a housing in which aredisposed a differential gear connected to a pair of wheels and adrive-mode-shifting mechanism; and the drive-mode-shifting mechanismincluding a movable member movable between a first position in whichtransmitted driving force from a power source is not transmitted to thedifferential gear or the wheels to effect a two-wheel-drive mode, asecond position in which the transmitted driving force from the powersource is transmitted to the differential gear to effect adifferential-free four-wheel-drive mode, and a third position in whichthe transmitted driving force from the power source bypasses thedifferential gear and is transmitted to the wheels to effect adifferential-lock four-wheel-drive mode.
 12. A driving forcetransmitting device for vehicle according to claim 11, wherein thedrive-mode-shifting mechanism includes a first rotating member formingan output member of the differential gear for one wheel side and asecond rotating member rotatable relative to the first rotating memberand rotatable together with one of the wheels, the second member beingcoaxial with the first member.
 13. A driving force transmitting devicefor vehicle according to claim 12, wherein the drive-mode-shiftingmechanism also includes a third rotating member rotatable together witha casing of the differential gear to which a driving force istransmitted from a power source.
 14. A driving force transmitting devicefor vehicle according to claim 13, wherein the first rotating member hasa surface provided with a first spline, the second rotating member has asurface provided with a second spline, the third rotating member has asurface provided with a third spline, and the movable member is providedwith a shift spline engageable with the first, the second and the thirdsplines.
 15. A driving force transmitting device for vehicle accordingto claim 14, wherein the first spline is provided on an outer surface ofthe first rotating member, the second spline is provided on an outersurface of the second rotating member, the third spline is provided onan inner surface of the third rotating member, the first splinepossesses a cross-sectional shape that is the same as thecross-sectional shape of the second spline, and the third spline isdisposed on an outer circumference of the first spline.